Members of the military, fire fighting personal and other emergency responders, and others who are required to operate in extreme temperature environments, for example, in the desert, near fires, or at latitudes approaching the Polar Regions, frequently rely on garments that have heat exchanging liquids flowing therethrough in order to maintain a safe body temperature. In addition, workers in hazardous chemical, thermal and manufacturing environments must wear personal protective equipment (PPE) to minimize their exposure to hazardous substances, however, the PPE can limit the body's ability to shed excess heat. Flexible heat exchangers have proven to be one of the most effective methods of adding or extracting heat from the human body. These garments include flexible tubing that is incorporated into the garment to carry cooling or heating fluids in close contact with the wearer's body. In general, heating or cooling garments are exemplified by U.S. Pat. Nos. 3,451,812; 3,425,486; 3,419,702; 4,691,762; 4,718,429; and 4,998,415. Other types of systems for body heating and cooling are illustrated in U.S. Pat. Nos. 4,114,620 and 5,062,424.
A liquid cooled garment (“LCG”) is an over-garment normally consisting of a fabric shell and a labyrinth of flexible tubing affixed in some fashion to the shell. LCG's are flexible heat exchangers used to assist in control of human body temperature where a person's physiology may not adequately control the body temperature because of the environmental conditions or because Personal Protective Clothing (PPE) is being worn. A liquid is cooled and circulated through the LCG. The liquid is cooler than the skin temperature of the user so that heat is transferred from the user to the liquid. Liquid chillers can be as simple as a water/ice bath or as complicated as a vapour compression refrigeration device. Whichever device is used, it lowers the temperature of the liquid below the skin temperature of the user and mechanically re-circulates the liquid through the LCG.
The conduit or tubing used in heat exchanging garments is typically formed from flexible polyvinylchloride (PVC), polyurethane, or similar polymers, which can be attached to the base fabric using any of three methods. The first and most common uses a standard zigzag sewing machine with a custom foot to keep the tubing centered. The second method, which was introduced by NASA, uses a base garment formed from a mesh material with the tubing “woven” through the fabric. The third and most current method was developed at the U.S. Army Garrison—Natick. This microclimate cooling garment (“MCG”), which is described in U.S. Pat. No. 5,320,164 of Szczesuil, et al., uses specialty tooling and fabric to create a two layer lamination with the PVC tubing locked between the layers in a complex pattern employing ten separate flow circuits. The Natick technology is the most widely deployed to date.
The MCG is designed to remove 180 watts of heat when fluid is circulated at a temperature of 65° F. and a rate of 12 gallons per hour. The MCG consists of two cooling panels, one that covers the front of the user's torso, and one that covers the back. Five hook and loop straps are located on the front panel for fit and size adjustment—three on the torso and one at each shoulder, as illustrated in FIG. 1.
The tubing network is distributed across the user's torso and is typically divided into ten parallel circuits. No matter how the cooling garment is constructed, all require the use of manifolds or miniature fittings to create individual flow circuits. An example of a simple multi-circuit construction is provided in FIG. 2, which illustrates a typical prior art tubing/manifold assembly with two four-port manifolds 2 and 4, for connection to inlet line 14 and outlet line 18, respectively, via barbed fittings 12 and 16. Manifold 2 has four ports 6a-6d, the barbed ends of which insert into tubes 8a-8d, respectively. The outlet ends of tubes 8a-8d are fitted over ports 10a-10d of manifold 4 after which the flexible tubing 8a-8d is secured to the manifold using a cyanoacrylate adhesive and a NYLON® cable tie (not shown). Such construction is intended to minimize back pressure (resistance to flow) and optimize heat transfer. Most cooling garments, whether zigzag sewn or woven, use miniature barbed fittings. The two cooling panels are attached to one another by a manifold pocket, which accommodates two manifold assemblies. The MCG uses a ten port barbed manifold, an example of which is shown in FIG. 3. Such manifolds provide the interface between the supply/return tubing and the individual tubing circuits. The manifold pocket and the supply/return tubing are located on the right side of a standard garment. An improved manifold with improved flexibility and reduced backpressure is described in co-pending application Ser. No. 12/910,821, which is incorporated herein by reference.
There are advantages to both sewn and laminated technologies. Referring to FIG. 4, laminated technology uses a “pattern board”, in which the circuit design is transferred to a flat plate 22 (normally phenolic) in the form of grooves 23 are machined into the board. Lightweight fabric 24, pre-coated with fusible material, is placed across the pattern board and tubing 28 is forced into the grooves, on top of the fabric 24. An outer layer 25 of fusible coated fabric (the coating is shown as a separate adhesive layer 26) is then placed over the tubing and the layers are subjected to heat and pressure to produce the lamination, thus sealing the tubing into the same pattern as the grooves.
One advantage of the laminated technology is that close radius bends can be formed without tubing distortion or kinking. Because the tubes are secured and supported in the grooves of the pattern board, the tubes retain their original aspect ratio until they are subjected to the heating process. During the heating process the tubing approaches the plastic temperature of the resin and the tubing is annealed to the new geometry. Because the tubing has been re-shaped by the annealing process, the short radius bends, on the order of 0.5 inch (˜12.7 mm), are stress relieved, as shown in FIG. 5.
Disadvantages of laminated technology include the cost of the tooling, including the pattern boards and thermal press, and the specialized treatment required for the fabrics to make them fusible. One pattern board is required for each front and back of each design/size. Most MCG designs are produced in at least three sizes, requiring a minimum of six pattern boards for production. For an efficient and cost-effective manufacturing process, three sets of pattern boards are needed, making a total of eighteen pattern boards for each design. Design changes to laminated MCG's can be costly and time consuming because the new design must be transferred to a machine program and new pattern boards fabricated. In addition, fabrics used in the lamination process include a fusible material (polyamide or polyurethane) to facilitate thermal lamination. This process is specialized and requires that large batches of fabric be treated to be cost effective. The lead time for the treatment may be weeks or months, such that accurate demand and manufacturing projections are required to meet production schedules.
Sewn technology is usually accomplished with a zigzag sewing machine. These machines are standard throughout the sewing industry and require only a custom presser foot, such as that shown in FIG. 6, to guide the tubing during the sewing process. One disadvantage to the sewn technology is that a long radius is required, as shown in FIG. 7. Any radius smaller than 0.75″ can distort and kink over time, which can restrict flow through the LCG circuit and adversely affect cooling performance.
One advantage to sewn technology is its simplicity. Although a custom presser foot is required, only standard sewing and marking equipment is necessary to produce reliable and repeatable results, an example of which is shown in FIG. 8. Design changes require only a revised pattern which can be quickly and cost effectively produced.
Given the drawbacks of the existing methods, the need remains for a method for manufacturing heat exchanging garments that is not limited by the radius bends in the tubing that carries the heat exchanging fluid.